Award Date

August 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry and Biochemistry

First Committee Member

Paul M. Forster

Second Committee Member

Frederic Poineau

Third Committee Member

Daniel Koury

Fourth Committee Member

Barbara Lavina

Fifth Committee Member

Pamela Burnley

Number of Pages

168

Abstract

The study of mater under extreme conditions has yielded fascinating insight into the physical and chemical nature of materials that under more modest conditions are considered mundane but have quite unusual properties when under pressure. Examples of this are the lightest of elements found in the first two rows and in the heaviest elements of the lanthanide and actinide series. Pure elements, though the simplest possible chemical systems, have proven to be among the most complex and interesting. Technetium metal is a simple HCP transition metal that, due to its half-filled d-shell, has a rich chemistry and an important place at the turning point for periodic trends in the transition metals such as melting point, elastic moduli and strength.

The objective of my research is to understand the high pressure behavior of technetium metal and the two oxides, TcO2 and Tc2O7. The project is separated into three emphases: equation-of-state of elemental technetium, phase stability of transition metal oxides (MO2, M= Tc, Re, Mo, W) and thermal motion of heptoxide species. Structural investigations are performed in diamond anvil cells (DACs) using synchrotron X-ray diffraction.

In the first portion, the goal is to define the ambient structure and the isothermal equation of state for technetium metal. This will be the basis for all other high pressure studies of technetium. The compression of technetium metal has been conducted using two pressure transmitting medium: MeOH-EtOH (67 GPa) and neon (153 GPa). In the second portion concerning the transition metal oxide, each dioxide was compressed. The compression data revealed trends in the anisotropic compression behavior of the monoclinic phases. A novel phase of MoO2 in the CaCl2 structure type was observed while decompressing from 60 GPa. In the third portion of this work, single crystal X-ray diffraction experiments were conducted from 100K through 280K for Tc2O7. Unanticipated apparent contractions in bond lengths with increasing temperature were identified as being due to liberational motion in the molecular solid, affecting both the terminal and the bridging oxygen atoms.

Keywords

Crystal Structure; Equation of State; Phase Transition; Technetium Dioxide; Technetium Heptoxide; Technetium Metal

Disciplines

Condensed Matter Physics | Inorganic Chemistry

Language

English


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